Paper No. 1
Presentation Time: 1:00 PM


WADE, Bridget S., Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, United Kingdom, KHALID, Abdul, School of Mathematics, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom and MOORE Jr, Ted C., Department of Earth and Environmental Sciences, University of Michigan, 2334 C. C. Little Building, 1100 North University Blvd, Ann Arbor, MI 48109,

The Eocene-Oligocene transition was a time of major climatic change, associated with extinctions of aquatic and terrestrial life forms, decrease in atmospheric carbon dioxide levels, drop in the calcite compensation depth and establishment of a continental ice-sheet on Antarctica. Integrated Ocean Drilling Program Expedition 320/321 recovered an expanded succession of Paleogene sediments in the equatorial Pacific Ocean. At Site U1334 there is a ‘bloom’ in the diatom species Coscinodiscus excavatusin the earliest Oligocene. The aim of this project was to document the size and abundance of these distinctive diatoms during a time of environmental change, with the following objectives:

1) Determine the distribution of Coscinodiscus excavatus from Site U1334

2) Document the maximum size of Coscinodiscus excavatus through quantitative morphometric analysis

3) Establish the timing and rapidity of size changes and relationship (if any) to environmental factors

Here we present quantitative abundance and morphometric analysis of 1200 specimens of Coscinodiscus excavatus from Site U1334. Samples were analysed at 1.5 metre intervals (90 kyr). Diatoms increase in size and abundance in the early Oligocene from 33.69 Ma. Specimens ranged in size from <120 microns to maximum sizes of 530 microns at 31.8 Ma. This was followed by a rapid decrease in size, with all specimens <150 microns from 31.10 Ma. Relative abundance data indicate a direct correlation between diatom abundance and maximum size. We use multispecies planktonic foraminiferal stable isotopes to reconstruct water column through this interval and explore the mechanism for the dramatic increase in diatom size in the earliest Oligocene.